1. Field of the Invention
The present invention relates generally to a gas turbine stationary blade, and more particularly, to a gas turbine stationary blade structured such that the shape of the blade leading edge is improved so as to blow a blade cooling air with an enhanced efficiency, a thermal stress concentration is avoided and a blade assembling is facilitated.
2. Description of the Prior Art
FIG. 6 is a cross sectional view showing a representative first stage stationary blade of a prior art gas turbine. In FIG. 6, numeral 20 designates a first stage stationary blade, numeral 21 designates an outer shroud and numeral 22 designates an inner shroud. Numerals 20a, 20b, 20c, 20d, 20e designate cooling air holes, respectively, wherein the holes 20a are provided in the blade leading edge, the holes 20b in the blade trailing edge, the holes 20c in the blade leading edge portion, the holes 20d in the blade central portion and the holes 20e in the blade trailing edge portion. Within the stationary blade 20, there are provided a passage 23 in the blade leading edge portion, a passage 24 in the blade central portion and a passage 29 in the blade trailing edge portion. An insert 25 is inserted into the passage 23 and an insert 26 is inserted into the passage 24. The inserts 25, 26 are provided in the passages 23, 24, respectively, with predetermined spaces being maintained from inner wall surfaces of the respective passages 23, 24 and are supported at a multiplicity of points. Both of the inserts 25, 26 are made in hollow cylindrical members and a multiplicity of air blowing holes 27, 28 are bored in and around entire walls of the inserts 25, 26, respectively.
In the above mentioned first stage stationary blade, cooling air 30, 31, 32 is led into the stationary blade 20 from a turbine casing space (not shown) through the outer shroud 21, wherein the cooling air 30 flows into the insert 25 on the leading edge side and then flows out of the air blowing holes 27 of the insert 25 into a space formed between an inner wall of the passage 23 and an outer wall of the insert 25 to effect an impingement cooling of the inner wall of the passage 23. The cooling air 30 then flows out of the cooling air holes 20c bored in the blade and onto an outer surface of the blade to effect shower head cooling and film cooling of the blade outer surface.
The cooling air 31 likewise flows into the insert 26 and then flows out of the air blowing holes 28 of the insert 26 into a space formed between an inner wall of the passage 24 and an outer wall of the insert 26 to effect the impingement cooling of the inner wall of the passage 24. The cooling air 31 then flows out of the cooling air holes 20d bored in the blade and onto the outer surface of the blade to effect film cooling of the blade outer surface. Also, the cooling air 32 flows into the passage 29 on the trailing edge side to cool a rear portion of the blade and flows out of the cooling air holes 20e of the blade trailing edge portion and onto the outer surface of the blade to effect film cooling thereof.
In the first stage stationary blade as described above, there occurs a non-uniformity of outflow air at the blade;s leading edge which causes an irregularity in the air flow velocity. This often results in an increased pressure loss or a back flow of the cooling air. There also occurs a clogging of the air blowing holes of the insert within the blade due to dust in the cooling air. This results in an increased pressure loss. Also, when the insert is to be assembled into the blade, there are a multiplicity of points to fix the insert in the air passage. Since the work space is narrow, assembling errors are more common and a lot of time is required for assembling the insert. Further, in terms of thermal stress, portions of the blade which are connected to the outer shroud and the inner shroud are structured so as to have only small fillet curves. As a result, thermal stress may concentrate in these areas and cause cracks. Thus, for a gas turbine that is operated at a higher temperatures, it is strongly desired to solve the above mentioned problems in order to enhance a reliability of the stationary blade.